The invention relates generally to the toners, and processes for making toners, useful in electrophotographic apparatuses. More particularly, the embodiments pertain to the addition of an embrittling agent to toner formulations to increase grinding rates.
Toner is commonly known as the “dry ink” for laser printers and copiers to form xerographic images on different substrates. It is typically comprised of a mixture of plastic resin, colorant and other toner ingredients and may be made mechanically, by grinding the ingredients into tiny particles. As xerographic processes become more advanced, the demand for high quality toner, comprising smaller particles, grows. Smaller particles are desirable because they provide sharper images as well as lower cost per image print.
However, the cost of producing toner with smaller particles by current technology can be very expensive. Most toner is made by “melt mixing” or “melt blending” the toner ingredients. For example, utilization of the extrusion process to prepare toner compositions is common. Extrusion is a continuous process that generally entails dry blending the toner ingredients, placing them into an extruder, melting and mixing the mixture, extruding the material, and reducing the extruded material to pellet form. The pellets are further reduced in size by grinding or jetting, and are then classified by particle size. A typical extrusion apparatus and process are described in U.S. Pat. No. 4,894,308, the disclosure of which is totally incorporated herein by reference. However, this process may sometimes be inexact and requires much energy. Further, the size produced varies throughout the grinding process and cannot be precisely controlled. To achieve particles that are uniform in size, the particles are mechanically sorted throughout the grinding process. Consequently, to achieve toner with average sized particles that are very small is expensive with traditional methods.
Although there are other methods of grinding that may be suitable for their intended purposes, such as for example, jetting where the strands are passed through the jets of an atomizer to break up the particles to the desired size, each method is generally energy intensive, and thus, costly.